1. Field of the Invention
The present invention relates to an apparatus for thermal analysis. Particularly, the present invention relates to an improved apparatus for thermal analysis which makes it possible to carry out thermally analytical measurement under an atmosphere comprising various kinds of gases such as a corrosive gas, a reactive gas and so on, which has been conventionally difficult or otherwise impossible.
2. Description of the Related Art
Thermal analysis has often been used in the fields of material analysis and product quality control because of its versatility and ease of measurement operations as well as the cost of the apparatus for the analysis being lower than that of other types of analytical apparatuses. Thus, thermal analysis has played an important role in both research and production activities.
Thermal analysis, as herein used, is intended to mean any analytical method in which a change of a structure and/or a physical property of a sample is detected under a regulated temperature condition. For example, differential thermal analysis (DTA), thermogravimetry (TG), differential scanning calorimeter analysis (DSC), evolved gas analysis (EGA) and so on are known as thermal analyses.
Among the above analyses, DTA and TG have been most popularly used. An apparatus which carries out a concurred TG-DTA analysis is also commercially available. Recently, an apparatus for TG-DTA analysis is often combined with a mass spectrometer (MS) so that function of EGA is additionally provided. The TG-DTA-EGA function is an extremely convenient and effective analytical method since an emitted gas from the sample as well as a heat balance and a weight change of a sample can be checked during a single measurement run.
By the way, thermal behavior of a sample during the thermal analysis thereof is closely related to the atmosphere which surrounds the sample. For example, when carbon is heated in the air, carbon dioxide is produced while an amount of heat is generated due to an oxidation reaction. However, when carbon is heated in an atmosphere of an inert gas such as nitrogen or helium, neither the production of carbon dioxide nor the heat generation occurs. Therefore, diagrams of the TG or the DTA measurements differ between an atmosphere of air and in that of inert gas.
Particularly, a weight change measured with TG reflects absorption of the atmosphere gas (optionally through a reaction) into the sample or gasification of a portion of the sample. Thus, with TG, the atmosphere surrounding the sample affects the results of measurement more severely than with the other thermal analyses.
Therefore, it is desirable that the thermal analysis be carried out in various atmospheres for the purpose of material research or obtaining product safety data as well as for the purpose of product quality control, However, a thermal analysis apparatus now commercially available is limited in its application to an atmosphere comprising air, nitrogen and so on, and it has been extremely difficult or otherwise impossible to use such an apparatus in other atmospheres comprising a corrosive gas such as chlorine gas.
The thermal analysis apparatus generally comprises a portion for the sample and a portion for signal detection. Since these portions are connected together, the atmosphere gas in the portion for the sample easily goes into the portion for the signal detection due to, for example, diffusion of the gas. When the corrosive gas is used as the atmosphere gas, the portion for the signal detection is damaged by the gas since such a portion is so sensitive to the gas, so that the measurement with the thermal analysis may become impossible.
In order to overcome the above problem, development of a thermal analysis apparatus has been carried out which allows thermal analysis under an atmosphere comprising corrosive gas. A structure of such an apparatus is schematically shown in FIG. 2 which shows a cross sectional view thereof. The apparatus (11) is constructed on the basis of an idea that an inert gas which flows from the portion for the signal detection (14) to the portion for the sample (12) is used as a carrier gas which carries the corrosive gas toward the portion for the sample (12). An inlet port of the inert gas (18) and an inlet port of the corrosive gas (17) are provided for the portion for the signal detection. However, since it is difficult to completely prevent back flow of the corrosive gas toward the portion for the signal detection in such a structure, an extremely large amount of the inert gas should be supplied so as to prevent back flow. Thus, it is substantially impossible to carry out thermal analysis under an atmosphere comprising a concentrated corrosive gas, which means that the apparatus cannot be multi-purpose, and there is a great bar against a multi-purpose apparatus.
As described above, thermal analysis is advantageous in that it is easy to carry out thermal analysis and and a variety of information is obtained, as well as the fact that the apparatus for thermal analysis is relatively inexpensive. Therefore, when thermal analysis can be carried out in the atmosphere comprising a corrosive gas, a reactive gas, an organic gas, a toxic gas and so on as well as in an atmosphere such as air which has been conventionally used, a great deal of advantage would be expected in the research and the production of the product.